The stem-II acid deposition and photochemical oxidant model—II. A diagnostic analysis of mesoscale acid deposition

The MesoSTEM model is used to analyse data obtained during the Mesoscale Acid Deposition Study. The Mesoscale Acid Deposition Study was designed to investigate acid deposition on the urban-suburban scale by sampling well defined frontal storms around the city of Philadelphia using a surface based network. The MesoSTEM model was developed to provide diagnostic analysis of these data. The mesoSTEM model is a combination of the Mesoscale Atmospheric Simulation System (MASS) predictive mesoscale dynamic meteorological model and the STEM-II model, a three-dimensional Eulerian acid deposition model. The MesoSTEM model is described in this paper and applied to the analysis of the 2 May 1985 storm. Elevated sulfate and nitrate deposition is predicted downwind of the major source areas and nitrate deposition exceeds that for sulfate. However, much of the NO_x and SO_x emitted on the mesoscale escapes the storm and becomes available for long-range transport and subsequent deposition.     

Transport and deposition of indoor radon decay products—I. Model development and validation

Commonly used mathematical models of indoor radon decay product behavior are based on macroscopic mass-balances, often referred to as ‘uniformly-mixed models’. The uniformly-mixed model's applicability is limited by its inability to track the movement of pollutants from their sources to other areas within the enclosure, to permit spatial- or time-dependent sources, or to take proper account of interactions with macroscopic surfaces. Although the uniformly-mixed model parameterizes the deposition process as a constant volumetric removal rate, in reality the deposition process is actually a surface phenomenon and is strongly affected by environmental conditions.This paper describes the development of RADTRAN, a two-dimensional radon progeny transport model that begins with the differential conservation equations describing the motion of air and the transport of reactive pollutants, introduces appropriate boundary conditions to represent surface deposition, and then calculates the concentration distribution of radon progeny throughout the entire region of interest. Knowing the concentration gradient near the surface, a local mass-transfer coefficient (the deposition velocity) can be determined as a function of environmental conditions. RADTRAN simulations have been based on several flow conditions: buoyancy-driven recirculating enclosure flows, free and forced-convection boundary layer flows, and one-dimensional diffusion. Free progeny diffusivity, D^f, and attachment rate, X, were varied over representative ranges. For these conditions, RADTRAN calculated free deposition velocities of u^f = 0.014–0.079 cm s⁻¹, for ²¹⁸Po. RADTRAN predictions are compared to a range of experimental measurements. It was found that the predicted range of deposition velocities is in rough agreement with findings from experiments conducted in flow conditions similar to the simplified flows used in RADTRAN.     

Transport and deposition of indoor radon decay products—II. Influence of environmental conditions

The effects of indoor radon decay product behavior on overall concentrations have generally been characterized using uniformly-mixed models, mathematical formulations based on steady-state macroscopic mass-balances, assuming uniform concentrations within the enclosure. The uniformly-mixed model parameterizes the deposition process as a constant volumetric removal rate, given different values for the free and attached progeny. The model requires prior knowledge of the deposition rates, and assumes them to be constant, independent of environmental conditions, and identical for all decay products. There has generally been little agreement regarding the actual values of the deposition rates, and the uncertainty in these required values presents an important limitation.In response to the limitations of existing mass-balance models, an indoor radon mass-transport model, RADTRAN, was developed using a microscopic mass-balance. Deposition by molecular diffusion is accounted for through boundary conditions, and deposition velocity is calculated based on the concentration distribution near the wall. Parametric sensitivity studies using RADTRAN examined the sensitivity of the deposition of radon decay products to several factors: the size of the free progeny (measured by its diffusivity, D^f), particle concentration (using the attachment rate, X), and air motion. Deposition is described in terms of the deposition velocities of the free and attached progeny, u^f and u^a. The development of RADTRAN is described in a companion paper. This paper presents the results of the parametric sensitivity studies examining the influence of environmental conditions on radon progeny deposition. Results primarily focus on the influence on the free mode of the first radon decay product, ²¹⁸Po. RADTRAN is also used to examine the variations of deposition velocity between the decay products.     

Multivariate geostatistical trend detection and network evaluation of space-time acid deposition data—I. Methodology

A multivariate geostatistical technique is presented to address two key issues of trend detection and network evaluation of acid deposition data. The proposed technique is specifically designed to be compatible with the distinctive characteristics of acid deposition variables such as non-stationary of their spatial means, non-stationary of their spatial covariances, their complex periodic and non-periodic temporal trends, and the common imbalance between the availability of their spatial and temporal data. To accomplish this, the time series at each measurement point is viewed as a separate, but correlated one-dimensional regionalized variable. Each variable is assumed to be a sum of periodic (e.g. seasonal) and non-periodic (e.g. anthropogenic) temporal random variables, each characterized by its own temporal variogram. To obtain an initial estimate of the frequency of the involved periodic trends, direct quadratic spectrum estimation is conducted. Based on fitted direct and cross variograms, various forms of estimation such as co-kriging of non-periodic components can be performed. The estimated time series may then be tested for the presence of long-term trends. In addition, the fitted sill values of any variogram model at different stations form elements of a coregionalization matrix. This matrix may be regarded as the variance-covariance matrix for the particular temporal-trend scale presented by the variogram model. A coregionalization matrix can be used to generate a spatial correlogram. Viewing the estimated integral scale of each spatial correlogram as an indicator of the radius of information-influence of each measurement station, a monitoring network can be evaluated for its adequacy of coverage at different temporal-trend scales. A coregionalization matrix can also be decomposed through principal-component analysis in order to determine any potential spatial groupings and/or to generate regional indicators of changes at different temporal scales.     

The stem-II regional scale acid deposition and photochemical oxidant model—IV. The impact of emission reductions on mesoscale acid deposition in the lower ohio river valley

Assessment of the effect of reduction in emissions of primary sources on eventual levels of pollutants, pH of precipitation and total wet deposition is crucial in designing acid-rain control strategies. The STEM-II/ASM model is used to investigate the effect of reduction in emissions on the ultimate deposition patterns and amounts of major acidic pollutants in a mesoscale region. This work also investigates the effect of background levels of primary pollutant species on the eventual levels and deposition amounts of SO₄⁼ and NO₃⁻. A series of mesoscale simulations were conducted in which emissions of primary sources of NO_x and SO₂ were reduced and/or background concentrations of certain key species were changed. The results indicate that the dominant effect on the eventual deposition amounts of SO₄⁼ and NO₃⁻ is due to background concentrations of key precursor species such as SO_x and NO_x. With relatively high background concentrations, reducing SO₂ emissions by 50% and NO_x emissions by 40% resulted in reductions of 2–3% for SO₄⁼ wet deposition aand about 15% for NO₃⁻ wet deposition. However, reducing the background concentrations of SO₂ and SO₄⁼ by 50% and NO, NO₂ and HNO₃ by 40% resulted in substantial reductions in wet deposition; SO₄⁼ deposition was reduced by 40–50% and NO₃⁻ deposition was reduced by approximately 35%.     

Trends in particulate deposition and precipitation chemistry at Leeds (U.K.) 1907–1987

A review of the available data on the composition of precipitation and the deposition rates of various species has been carried out for the city of Leeds in Northern England covering the years 1907–1987. The information for three typical sites representing heavily industrialized, suburban and rural locations is compared. The exceptionally high deposition rates and large urban/rural differences of the early years have now disappeared. Perhaps surprisingly, the parameter which has changed least is the net acidity. The highly acidic deposits of sulphates and chlorides from coal combustion before 1930 were counterbalanced by correspondingly high deposition rates of ammonia and alkaline dusts. The only major parameter which shows a significant increase in nitrate.     

Unified wet deposition data summaries for North America: Data summary procedures and results for 1980–1986

This paper presents a framework for data quality assessment of annual and seasonal precipitation chemistry data summaries. Consideration has been to (i) using data from regional or national networks with established quality assurance/quality control programs and well documented network operation protocols, (ii) assessing regional representativeness of each sites, (iii) determining quantitative measures to define data completeness levels, and (iv) documenting the calculation procedures used to compute precipitation-weighted mean concentrations and wet deposition amount. The procedures described here are applied to data collected from 1980 to 1986 by five major acid deposition monitoring networks in North America and examples of annual sulfate deposition summaries are reported. It is recommended that the concepts of site representativeness, data completeness and overall data quality levels be adopted by the user community and routinely be reported along with a data summary. Further work on assesing accuracy and precision to accompany the data quality levels is recommended.     

Regional pattern of mercury wet deposition in Beijing

ＩｎｔｒｏｄｕｃｔｉｏｎＲｅｃｅｎｔｆｉｎｄｉｎｇｓｆｒｏｍｍｅｒｃｕｒｙｒｅｓｅａｒｃｈｉｎｄｉｃａｔｅｔｈａｔｔｈｅｍａｊｏｒｓｏｕｒｃｅｔｏｌａｋｅｓｉｓａｔｍｏｓｐｈｅｒｉｃｄｅｐｏｓｉｔｉｏｎ(Ｓｏｒｅｎｓｅｎ ,1990 ;Ｇｌａｓｓ,1990 ) ,ａｎｄｔｈａｔｓｉｇｎｉｆｉｃａｎｔｓｏｕｒｃｅｓｔｏｔｈｅａｔｍｏｓｐｈｅｒｅａｒｅｆｏｓｓｉｌｆｕｅｌｃｏｍｂｕｓｔｉｏｎａｎｄｉｎｃｉｎｅｒａｔｉｏｎｏｆｍｕｎｉｃｉｐａｌｓｏｌｉｄｗａｓｔｅａｎｄｓｌｕｄｇｅ(Ｇｌａｓｓ,1991;Ｗｈｉｔｅ ,1992 ;Ｃ…     

Influence of acid deposition on atmospheric corrosion of zinc

Site exposure tests both open and sheltered have been carried out in acid deposition area in Southwest China. Results from six sites show that acid deposition exerts a great influence on atmospheric corrosion of Zn, and it is more serious in wet condition. Basically, Zn corrosion is directly proportional to time of exposure. While SO2 is the main pollutant of the atmosphere environment, Zn corrosion has a linear relationship to SO2 depositing rate and a hyperbolic to rain pH value.Observations by SEM, EDAX and X-ray diffraction show that under sheltered exposure condition, the corrosion products of Zn in heavy acid deposition area principally are sulphates.Based on the corrosion rates measured, the working life of galvanized steel can be predicated.     

Effects of acid deposition on forests in south China

１ＩｎｔｒｏｄｕｃｔｉｏｎＷｉｔｈｔｈｅｆａｓｔｇｒｏｗｉｎｇｏｆｍｏｄｅｒｎｉｎｄｕｓｔｒｙａｎｄｓｈａｒｐｌｙｉｎｃｒｅａｓｉｎｇｏｆｅｎｅｒｇｙｃｏｎｓｕｍｐｔｉｏｎｐｒｉｍａｒｉｌｙｃｏａｌ，ａｉｒｐｏｌｕｔｉｏｎａｎｄａｃｉｄｄｅｐｏｓｉｔ...     

The buffering effects of aquatic sediments against acidic deposition

ＴｈｅｂｕｆｆｅｒｉｎｇｅｆｆｅｃｔｓｏｆａｑｕａｔｉｃｓｅｄｉｍｅｎｔｓａｇａｉｎｓｔａｃｉｄｉｃｄｅｐｏｓｉｔｉｏｎＬｉａｏＢｏｈａｎ；ＴａｎｇＨｏｎｇｘｉａｏ（ＲｅｓｅａｒｅｈＣｅｎｔｅｒｆｏｒＥｃｏ－ＥｎｖｉｒｏｎｍｅｎｔａｌＳｃｉｅｎｃｅｓ...     

Effect of acidic deposition on productivity of forest ecosystem and estimation of its economic losses in southern suburbs of Chongqing

In accordance with principle sand methods of ecology, this paper studied the effects of acidic deposition on productivity and volume increment of masson pine and Cinnamomum campora forest which are widely distributed in southern suburbs of Chongqing. Based on the field data and measurements, a multivariable stepwise regression model was established to analyze the effects of multiple environmental factors on the productivity of the forest ecosystems. This model was used to assess the volume and economic losses of these two forest ecosystems caused by acidic deposition. The results showed that, among the environmental factors, pH value of precipitation, soil depth, soil organic contents and slope are the dominant ones influencing the growth of masson pine forest. It is also shown that the acidic deposition has no clear relation to the growth of C.Campora forest, so development of such broad-leaved forest is suitable in the area.     

Aspects of wet,acidifying deposition in Arnhem: Source regions,correlations and trends (1984–1991)

A time series of wet deposition in Arnhem, the Netherlands, was analysed for the period 1984–1991. Precipitation was collected with four samplers on a daily basis. A comparative study by the Dutch National Precipitation Network showed significant biases for the observations of the National Network station due to longer exposure to dry deposition. Simultaneous operation of wet-only and bulk collectors demonstrated a concentration bias of about 10% for daily bulk sampling.Using a cluster analysis of backward trajectories, clear distinctions could be made between precipitation from continental and maritime origin. Event-to-event variations in deposition seemed to be determined largely by meteorological influences. As major anthropogenic source regions, the U.K., France, Belgium and the Netherlands itself were identified. The contribution of Dutch sources to wet acid deposition in Arnhem was estimated at 30–40%.Trends and seasonal variations were analysed with an advanced time-series model based on Kalman filtering. Similar seasonal variations were found for SO₄²⁻ and NH₄⁺. Also, seasonal variations in the concentrations of H⁺ and NO₃⁻ corresponded. Significant long-term changes in deposition and concentration were found for SO₄²⁻ (about −3% yr⁻¹) and H⁺ (about −9% yr⁻¹) only. The analysed trends were decreasing, but decreases were larger in the years 1984–1986 than in the following years. The relative decrease in the wet deposition of SO₄²⁻ was substantially smaller than decrease in dry-deposited SO₂ and SO₄²⁻.     

A database of modeled gridded dry deposition velocities for 45 gaseous species and three particle size ranges across North America

The dry deposition process refers to the?ux loss of an atmospheric pollutant due to uptake of the pollutant by the earth’s surfaces.Dry deposition?ux of a chemical species is typically calculated as the product of its surface-layer concentration and its dry deposition velocity(V_d).Field measurement based V_ddata are very scarce or do not exist for many chemical species considered in chemistry transport models.In the present study,gaseous and particulate dry deposition scheme...     

Multivariate geostatistical trend detection and network evaluation of space-time acid deposition data—II. Application to NADP/NTN data

A multivariate geostatistical technique was presented in the first part of this paper (Rouhani et al., 1992, Atmospheric Environment 26A, 2603–2614) with the objective of addressing two key issues of trend detection and network evaluation of the acid deposition data. The investigated data include weekly reported SO₄²⁻ concentrations and depositions from 34 level-1 stations of the NADP/NTN. The duration of the available data ranges from 6 to 10 years. In order to extract the maximum amount of information from these relatively short time series, it is imperative to avoid any data reduction, such as integrating the data into seasonal or annual series. Direct quadratic spectrum estimation is applied to the data, which clearly indicates the presence of annual cycles in a large number of stations. Based on these preliminary results, measurement stations are grouped into three main eco-regions, including the Northeast/central, the West and the Midwest/Gulf regions. While the first two regions exhibit significant annual periodicities, the latter region does not show any significant cyclic characteristics. This analysis is followed by multi-scale temporal variography that further confirms the presence of periodic trends. Two types of time series are generated by co-kriging: (1) the non-periodic components at each station, and (2) the non-periodic regionalized factors for each region. Kendall's test for trend detection is applied to all generated time series, as well as to the original data. The results indicate that by geostatistical filtering of periodic components, the proposed procedure offers an efficient technique for trend detection. Using the estimated coregionalization matrices, spatial correlograms are generated for various temporal scales and regions. Viewing the estimated integral scale of each spatial correlogram as an indicator of the radius of information-influence of each measurement station, the NADP/NTN network is evaluated for its adequacy of coverage under different temporal scales.     

Critical load of sulfur deposition for ecosystemand its application in China

ＣｒｉｔｉｃａｌｌｏａｄｏｆｓｕｌｆｕｒｄｅｐｏｓｉｔｉｏｎｆｏｒｅｃｏｓｙｓｔｅｍａｎｄｉｔｓａｐｐｌｉｃａｔｉｏｎｉｎＣｈｉｎａＺｈａｏＤｉａｎｗｕ；ＺｈａｎｇＸｉａｏｓｈａｎ；ＹａｎｇＪｉａｎｘｉｎ（ＲｅｓｅａｒｃｈＣｅｎｔｅｒｆｏｒＥｃｏ－Ｅ...     

Effect of acidic deposition on productivity of forest ecosystem and estimation of its economic losses in southern suburbs of Chongqing, China

ＥｆｅｃｔｏｆａｃｉｄｉｃｄｅｐｏｓｉｔｉｏｎｏｎｐｒｏｄｕｃｔｉｖｉｔｙｏｆｆｏｒｅｓｔｅｃｏｓｙｓｔｅｍａｎｄｅｓｔｉｍａｔｉｏｎｏｆｉｔｓｅｃｏｎｏｍｉｃｌｏｓｅｓｉｎｓｏｕｔｈｅｒｎｓｕｂｕｒｂｓｏｆＣｈｏｎｇｑｉｎｇ，ＣｈｉｎａＷｕＧａｎｇ...     

Low-cost automated rain collector and its application to the study of wet only deposition in São Paulo (Brazil)

An automatic rain collector was developed with emphasis on simplicity, construction with readily available low-cost materials, inexpensive maintenance and reliable operation at temperatures above freezing point. The rain sensor is of the heated AC conductometric type and the circuit includes electronic protections against false triggering by electrical transients. With this collector, the first studies of chemical characterization of wet only deposition were made in São Paulo over the period of November 1988 to June 1990. Results are presented and compared with previous total deposition studies. For this period the volume-weighted mean values of the pH and conductivity were 4.6 and 19 μS cm⁻¹, respectively.     

Relative sensitivities of woody plants to acid deposition in south areas of China

Relative sensitivities of 30 species of common woody plants to simulated acid rain with pH values of 2.0, 2.5, 3.0, 3.5, 4.5 and control were studied. The results showed that 6 species of these plants were sensitive to simulated acid rain. The moderate included 18 species. The resistant included 6. Relative sensitivities to ambient acid rain and air pollutants and visible injury degree of 30 species of common woody plants in Chongqing City were investigated. Results showed that 6 species with foliage lesion rate at above 10 percent were sensitive, that 6 species with no lesion were resistant and that other 18 species with lesion at 10 percent below were moderate. Other 7 cities (Guiyang, Zunyi, Duyun, Changsha, Zhuzhou, Liuzhou and Guilin City) were also investigated and results were consistent with those of Chongqing City. The experimental and investigated results showed relative sensitivities and visible injury degree of woody plants to simulated acid rain were consistent with those of the woody plant     

Dry deposition of atmospheric aerosols by dual tracer method — I. Area source

Aerosol deposition velocities can be estimated from measurements of the ratio of the concentration of a depositing species, such as Pb, to a non-depositing (conserved) species, such as CO, when both originate from the same source (dual tracer method). This method has been applied to size-segregated aerosol samples collected in Los Angeles, CA during the Southern California Air Quality Study, summer 1987. Lead size distributions were measured in ambient and tunnel samples using an eight-stage low pressure impactor. A new parameter, the fraction of aerosol remaining airborne, was directly determined. This fraction is of great importance receptor modelling. Dry deposition velocities calculated using a stirred atmosphere (box) model, varied over three orders of magnitude depending on particle size. The calculated deposition velocity for unit density particles > 0.5 μm, was approximately proportional to D_p² as expected for deposition by an interception mechanism (d_p = particle aerodynamic diameter).